1. Field of the Invention
The present invention relates to a liquid crystal display device for realizing a large surface display screen, and more particularly to a liquid crystal display device for realizing a large surface display screen by means of enhancing a uniformity of a luminance through a plurality of light supply members.
2. Description of the Related Art
In general, a liquid crystal display device displays an image through a modulation of a light by a liquid crystal cell formed therein, after an orientation of a liquid crystal is changed by applying a voltage and optical characteristics of the liquid crystal such as birefringence, optical activity, bicolor property or scattering are converted into visible variations by means of a specific orientation of the liquid crystal.
The liquid crystal display devices are divided into a twisted nematic (TN) type liquid crystal display device and a super-twisted nematic (STN) type liquid crystal display device. Also, liquid crystal display devices are divided into an active matrix display type including switching devices and a TN liquid crystal, and a passive matrix display type having a STN liquid crystal in accordance with operations of the liquid crystal display devices. A thin film transistor liquid crystal display device (TFT-LCD) has thin film transistors (TFT) as the switching devices, and the thin film transistor liquid crystal display device is widely utilized for a monitor because the thin film transistor liquid crystal display device has a simplified construction.
The liquid crystal display device generally has a liquid crystal display panel including a liquid crystal for determining a transmissivity of a light after receiving an electrical signal. A back light assembly is installed at a rear face of the liquid crystal display panel of the liquid crystal display device because the liquid crystal display device is a passive device that does not emit a light for itself.
A source part and a gate part are formed on the liquid crystal display panel. The source part includes a source driving integrated circuit (IC) for applying image data for displaying an image, and the gate part has a gate driving integrated circuit for applying gate signals for driving thin film transistors formed on the liquid crystal display panel. Image signals applied from an outside are converted into data signals for driving the liquid crystal display panel and the gate signals for driving the thin film transistors through a printed circuit board. Those data and gate signals are applied to the thin film transistors on the liquid crystal display panel via the source and the gate parts. Hence, a liquid crystal of the liquid crystal display panel receives electrical signals, thereby displaying images using lights generated from the back light assembly.
As it is described above, the back light assembly provides the liquid crystal display panel with uniform lights, and the back light assembly has a lamp for generating a light, a light guiding plate for guiding the light from the lamp, and a lamp housing disposed by the side of the light guiding plate for enclosing the lamp.
A cold cathode ray tube is utilized as the lamp. After the light emitted from the lamp passes through a lateral portion of the light guiding plate, and then the light is converted into a planar light using the light guiding plate. A diffusion sheet and a prism sheet are disposed between the light guiding plate and the liquid crystal display panel for maintaining a uniformity of the light inputted into the liquid crystal display device.
Recently, a size of the liquid crystal display device increases according as an electronic apparatus such as a computer or a projection television have large sizes. Also, a dimension of the back light assembly increases in accordance with an augmentation of the size of the liquid crystal display panel. The conventional back light assembly having one light source, however, cannot assure the uniformity of the light for realizing the large surface display screen. Hence, a back light assembly including a plurality of lamps has been developed.
For example, a back light assembly having two lamps is disclosed at U.S. Pat. No. 5,046,826 issued to Ilirofumi Iwamoto et. al.
FIG. 1 is a cross-sectional view showing the back light assembly disclosed at the above U.S. patent.
Referring to FIG. 1, the back light assembly 10 includes a light-transmitting member 15 such as a light guiding plate.
Grooves or holes are formed in a bottom face of the light-transmitting member 15, and the grooves or the holes are formed as hollow spaces for receiving light sources 20. A reflection plate 25 is disposed to enclose the bottom face and lateral portions of the light-transmitting member 15 besides an upper face of the light-transmitting member 15 through which a light passes. The light-transmitting member 15 and the reflection plate 25 are fixed using a housing 30.
A light screen 35 is formed at a portion of the light-transmitting member 15 through which the light passes, and the light screen 35 is composed of an opaque material disposed as a dotted pattern. A light scattering member 40 is formed on the light screen 35, and a liquid crystal display panel 45 is formed on the light scattering member 40 for forming an image.
A light 50 generated from the light source 20 advances through the light-transmitting member 15 toward the light screen 35, and a light 51 downwardly advancing from the light source 20 is reflected by the reflection plate 25, thereby advancing into the light-transmitting member 15. After the lights 50 and 51 are modulated by the light screen 35, the lights 50 and 51 are converted into scattering lights by means of the light scattering member 40, and then inputted into a rear face of the liquid crystal display panel 45.
However, though a large surface display screen may be realized with the back light assembly having the above-mentioned construction, the light-transmitting member 15 should have a thick thickness because the lights inputted into the liquid crystal display device 45 must be uniform. Thus, the back light assembly 10 should have a thick thickness in accordance with an augmentation of the thickness of the light-transmitting member 15.
Also, the lights inputted into the liquid crystal display panel 45 may not be uniform and a quantity of lights directly inputted into the liquid crystal display panel 45 from the light source 20 is larger than that of other portions and an intensity of the lights adjacent to the lamps is larger than that of the other portions.
The present invention has been made to solve the aforementioned problem, and accordingly it is an object of the present invention to provide a back light assembly including a light guiding plate having a greatly reduced thickness and providing a liquid crystal display panel with a uniform light.
It is another object of the present invention to provide a liquid crystal device realizing a large surface display screen by means of a plurality of light control members in order to enhance a luminance uniformity of a light.
To achieve one object of the present invention, there is provided a liquid crystal display device comprises a back light assembly and a display unit. The back light assembly has a light source for generating a light, a light guiding plate formed at least at one portion of the light source for converting the light generated from the light source into a planar light having a uniform luminance and advancing in a first direction, and a light control member formed between the light guiding plate and the light source for preventing the light from directly advancing in the first direction. The display unit forms an image using the light that advances in the first direction from the light guiding plate.
Preferably, the light control member is comprised of semitransparent or opaque materials, and the light control members have band shapes that are disposed along the first direction.
A groove for receiving the light source is formed at the light guiding plate along in a second direction opposite to the first direction, and the light control members are disposed in the grooves. In this case, the light source is inserted into lamp fixing members installed in the grooves, and is fixed in the lamp fixing member.
In one preferred embodiment of the present invention, a first slope of the light guiding plate formed between the light source and an adjacent light source is smaller than a second slope at the peripheral portion of the light guiding plate from the light sources so that the light guiding plate has a thickness which becomes thinner from the light source. In another preferred embodiment of the present invention, the light guiding plate has a constant thickness without regard to a distance from the light source.
According to the present invention, a liquid crystal display device can have much simplified construction and the liquid crystal display device can be easily manufactured by means of improving a structure of a light supply unit having a back light type. Also, a light guiding plate can have greatly reduced thickness by forming light control members and the light guide plate having a function of a housing over light sources, and the liquid crystal display device can have a large surface display screen because a luminance of an image displayed on the screen can be maintained uniform by means of uniformly maintaining a luminance of light emitted from the light sources without additional reflection members. Furthermore, the light supply unit can have a proper dimension in accordance with a variation of shapes or sizes of the liquid crystal display device because the light supply unit can have various shapes.